THE MAIN FACTORS AFFECTING THE RATE OF SEPARATION OF THE SLAG AND MATTE PHASES BY THEIR DENSITY: A GENERAL OVERVIEW

ABSTRACT

The article discusses the main factors affecting the rate of separation of the slag and matte phases by their density, one of the urgent problems of copper production. The results of the analysis showed that during the processing of sulfide copper concentrates in melting furnaces, due to the high partial pressure of oxygen, a large amount of magnetite compound appears in the system, which increases the density of the slag. An increase in slag density slows down the separation of the slag and matte phases. As a result, the loss of copper with slag increases, which leads to a decrease in the productivity of the furnace for copper. 

АННОТАЦИЯ

В статье рассмотрены основные факторы, влияющие на скорость разделения шлаковой и штейновой фаз по их плотности, одной из актуальных проблем медного производства. Результаты анализа показали, что при переработке сульфидных медных концентратов в плавильных печах из-за высокого парциального давления кислорода в системе появляется большое количество соединения магнетита, что увеличивает плотность шлака. Увеличение плотности шлака замедляет разделение шлаковой и штейновой фаз. В результате увеличиваются потери меди со шлаком, что приводит к снижению производительности печи по меди.

Keywords: magnetite, copper, density, slag, matte, phase separation, copper loss, matte droplets.

Ключевые слова: магнетит, медь, плотность, шлак, штейн, разделение фаз, потери меди, штейновые капельки.

One of the main reasons why copper remains in the converter slag in large quantities is the increased density of the slag [1]. The substance that increases the density of converter slag is magnetite [2]. In order to determine the specific density of the converter slag selected for the study, its mineralogical composition was first determined [3]. The material composition of the converter slag selected for the study is presented in Table 1 [4].

Table 1.

Mineralogical composition of the converter slag of “Almalyk Mining and Metallurgical Combine” selected for the experiment, %

Based on the material composition presented in Table 1, the density of the converter slag was determined using the specific densities of each substance listed in Table 2 [5].

Table 2.

Densities of the main components in converter slag of “Almalyk Mining and Metallurgical Combine” selected for the experiment, g/cm³

Using the individual densities of each component given in Table 2, the average densities of converter slags selected as research objects were determined by the following formula [6]:

ρ_slag = (ω₁·ρ₁ + ω₂·ρ₂ +… + ω_n·ρ_n)/100                             (1)

Here: ω₁, ω₂, and ω_n are the respective mass fractions of each component that makes up the slag, %; and ρ₁, ρ₂, and ρ_n are their respective individual densities, g/cm³.

Using the formula (1), average densities of converter slags with different magnetite content obtained for the study were determined and these values are listed in Table 3 [7].

Table 3.

Changes in the densities and the amount of copper compounds in the order of increasing magnetite content in the converter slag of “Almalyk Mining and Metallurgical Combine” selected for the experiment

The values in Table 3 indicate that an increase in the amount of magnetite in the slag causes an increase in its overall density [8]. It can be seen from the graph shown in Figure 1 that increasing the amount of magnetite leads to a linear increase in the density of the slag [9].

Figure 1. Dependence of slag density on the amount of magnetite in converter slag

An overabundance of magnetite in the slag causes several magnetite crystals to coalesce to form a larger magnetite crystal [10]. In this case, the density of large magnetite particles is higher than the density of slag, but close to the density of matte, so they sink to the bottom of the slag layer and accumulate at the boundary of the slag and matte phase separation (Fig. 2).

Figure 2. Scheme of formation of magnetite layer between the contact boundary of slag and matte

As shown in Figure 2, the magnetite layer formed at the interface between the slag and matte prevents the small matte droplets in the slag phase from passing into the main matte phase below. This increases the mechanical loss of copper with slag [11].

In the diagram in Figure 3, it can be seen that as the amount of magnetite in the slag phase increases, the amount of copper sulfide decreases and the amount of copper oxide increases. This causes an increase in the chemical loss of copper. Because the surface tension of oxidized copper compounds is very different from the surface tension of matte, it is similar to the surface tension of slag and therefore remains in the slag phase. 

The relative density of matte droplets suspended in the slag phase and the corresponding concentrations are presented in Table 4.

Figure 3. The dependence of the percentage of the main components affecting the density of the converter slag on the amount of magnetite: 1-Cu₂S, 2-Cu₂O and 3-FeS

Table 4.

Value of density of matte droplets with different composition

Figure 4. Changes in the density of the matte with increasing copper content in the matte

From the values in Table 4 and the graph in Figure 4, it can be seen that the more copper content the matte has, the higher its density. For example, when the content of copper in matte reached 37.18%, its density reached a maximum of 5.29 g/cm³.

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